1. Field of the Invention
The present invention relates to flow rate ratio controllers, used in semiconductor manufacturing processes, which branch at a desired ratio a flow of source gases.
2. Description of the Background Art
In the field of the semiconductor manufacturing process in recent years, along with an increase in wafer size, the size of the processing chambers containing the wafers has also been increased. Meanwhile, when films are deposited on semiconductor wafers, the source gases for the deposition preferably have a uniform concentration; however, if the source gases are introduced into one of these larger-sized processing chambers through only one location, the concentration distribution may become partially unbalanced.
For this reason, more recently, processing chambers have been adapted so as to incorporate a plurality of gas inlets, and fed through the respective inlets with source gases at a mass flow ratio that is controlled such that the gas concentration in the chamber is made uniform. In this case, as a device for branching the flow of the source gases at a desired ratio, a flow rate control device is used.
FIG. 5 illustrates an example of a conventional flow rate ratio control device 100X of a two-branch-flow type. In FIG. 5, reference symbol RXM represents a main channel into which gas flows. The main channel RXM is provided with a pressure sensor 4X, and an end thereof is branched into two. In the branched branch channels RX1 and RX2, flow rate meters 21X and 22X, and control valves 31X and 32X are respectively provided in series. Also, a valve control section 5X monitors units of flow rate data outputted from the respective flow rate meters 21X and 22X, and pressure data outputted from the pressure sensor, and on the basis of values from the respective units of data, controls the control valves 31X and 32X such that ratios of mass flow rates of gas flowing through the respective branch channels RX1 and RX2 to the total flow rate (referred to as flow ratios) become equal to given predetermined ratios.
Specifically, the valve control section 5X firstly performs feedback control of the control valve 31X in one of the branch channels RX1 such that the value from the above-described pressure data (also referred to as measured pressure) becomes equal to a predetermined constant target pressure. Then, under the condition that the measured pressure is controlled to be near or not less than the target pressure, the valve control section 5X performs feedback control of the other control valve 32X such that the ratios of the values of the units of flow rate data (measured flow rates) to the total flow rate become equal to the predetermined ratios.
Patent document 1: Japanese Unexamined Patent Publication No. 2005-38239